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    Layers of The Earth

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    MedicareMinstun Project
    The Earth is composed of three main compositional layers: the crust, mantle, and core. The crust is the outermost layer and is made up of silicate rock, ranging from 5-70 km thick. Below the crust is the mantle, which is over 2900 km thick and composed of ultramafic silicate rock. The innermost layer is the core, which is liquid on the outside and solid on the inside, and composed of iron and nickel. These layers have distinct boundaries and compositions. The Earth also has five mechanical layers that differ in strength - the lithosphere, asthenosphere, lower mantle, outer core, and inner core.

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    Layers of The Earth

    Uploaded by

    MedicareMinstun Project
    31 views2 pages
    The Earth is composed of three main compositional layers: the crust, mantle, and core. The crust is the outermost layer and is made up of silicate rock, ranging from 5-70 km thick. Below the crust is the mantle, which is over 2900 km thick and composed of ultramafic silicate rock. The innermost layer is the core, which is liquid on the outside and solid on the inside, and composed of iron and nickel. These layers have distinct boundaries and compositions. The Earth also has five mechanical layers that differ in strength - the lithosphere, asthenosphere, lower mantle, outer core, and inner core.

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    Layers of the Earth

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    Layers of the Earth

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    The Earth is composed of three main compositional layers: the crust, mantle, and core. The crust is the outermost layer and is made up of silicate rock, ranging from 5-70 km thick. Below the crust is the mantle, which is over 2900 km thick and composed of ultramafic silicate rock. The innermost layer is the core, which is liquid on the outside and solid on the inside, and composed of iron and nickel. These layers have distinct boundaries and compositions. The Earth also has five mechanical layers that differ in strength - the lithosphere, asthenosphere, lower mantle, outer core, and inner core.

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    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    31 views2 pages

    Layers of The Earth

    Uploaded by

    MedicareMinstun Project
    The Earth is composed of three main compositional layers: the crust, mantle, and core. The crust is the outermost layer and is made up of silicate rock, ranging from 5-70 km thick. Below the crust is the mantle, which is over 2900 km thick and composed of ultramafic silicate rock. The innermost layer is the core, which is liquid on the outside and solid on the inside, and composed of iron and nickel. These layers have distinct boundaries and compositions. The Earth also has five mechanical layers that differ in strength - the lithosphere, asthenosphere, lower mantle, outer core, and inner core.

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    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
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    Compositional Layers

    The Earth is a sphere of radius 6371km which is stratified or layered. Compositional layers differ
    in chemical composition. The Earth has three compositional layers:

    1. The crust: low density silicate rock, 5-70 km thick. There are two distinct types of crust.
    a. Continental crust is variable in thickness and composition. Thickness ranges
    from 5-70 km. The composition ranges from mafic to felsic.
    b. Oceanic crust is uniform in thickness and composition. It is 5-6 km thick and is
    mafic in composition.
    c. The differences in thickness and density between continental and oceanic are
    responsible for the existence of ocean basins due to isostatic balance as the crust
    floats on the more dense mantle.
    2. The mantle: high density, ultramafic silicate rock which can flow when subjected to
    long duration stresses. The mantle is over 2900 km thick and makes up over 80% of the
    volume of the Earth. The mantle is not molten!
    3. The core: iron and nickel, liquid outer region with a solid center. The core is just over
    half the diameter of the Earth.

    These compositional layers have sharp or abrupt boundaries between them.

    Whole earth composition is estimated from unbiased samples of meteorites. Earth


    structure is obtained by combining this with seismic data.

    Motion of liquid iron and nickel in the outer core gives the Earth a dipole magnetic field, nearly
    aligned with the rotational axis. The magnetic field of the Earth reverses spontaneously at
    random times. Over the last several million years, the average time between reversals has been
    about 200,000 years. The last reversal was 730,000 years ago. Reversals probably take less that
    5,000 years. Reversals of the field probably involve a period of time where the field weakens
    substantially and becomes disorganized (non-dipole), then reorganizes in the opposite polarity.
    People should wear lead underwear during a reversal, as the Earth's surface will be bombarded
    with a higher than normal amount of cosmic radiation!

    Mechanical Layers

    In addition to the compositional layers, the Earth has mechanical layers. Mechanical
    layers differ in their strength or rigidity. These layers do not correspond on a one-to-
    one basis with the compositional layers. The Earth has five mechanic layers:

    1. The lithosphere is the outermost mechanical layer and is the most rigid layer
    of the Earth. The lithosphere consists of the crust, and some of the uppermost
    mantle. The lithosphere averages about 100 km thick. It is somewhat thicker
    beneath continents, and dramatically thinner under mid-ocean ridges.
    2. The asthenosphere lies beneath the lithosphere. It is a part of the mantle,
    approximately 100 km thick, with very little strength. The asthenosphere flows
    relatively easily and accomodates the movement of the overlying lithosphere.
    The upper and lower boundaries of the asthenosphere are diffuse as they
    involve gradual changes in the rigidity of the mantle, not a change in
    composition.
    3. The lower mantle or mesosphere consists of most of the mantle. This part of
    the mantle flows, but at much slower rates than the asthenosphere.
    4. The outer core is liquid iron (with some nickel and other elements). This is the
    only internal layer of the Earth that is a true liquid. The core-mantle boundary
    is the one mechanical boundary that is also a compositional boundary.
    Movement of the electically conductive fluid in the outer core generates the
    Earth's magnetic field.
    5. The inner core is solid. It has the same composition as the outer core, and is
    about half the diameter of the core.

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